iTunes Tune Up

It's very simple it checks yours songs in on your computer filling in the missing gaps.
So if a track is missing the song name, artist, album artwork, lyrics, genre looks them up and does the work.

It's not fast but is works, analysing the music's digital fingerprint so it never gets it wrong.

You don't pay for the App. you pay for the service costing $10 a year.

I heard about it a while ago but it got pulled down before I could try it.
Written by three students in the States, it was originally given it away free but the costs where to high for them to sustain as they had to pay for access to the various databases needed.
Well they are back.